correct array indices / size

```C++
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE][MAX_KEY], 0); // is wrong
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE-1][MAX_KEY-1], 0); // looks better but is still wrong
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE][MAX_KEY-1], 0); // is also wrong
std::fill(&Key2Event[0][0], &Key2Event[MAX_MODE-1][MAX_KEY], 0); // is correct but looks weird ;-)
```